The public definition of sepsis, as determined by a gathering of international experts at the Merinoff Symposium 2010 is: Sepsis is a life threatening condition that arises when the body's response to an infection injures its own tissues and organs. Sepsis leads to shock, multiple organ failure and death especially if not recognized early and treated promptly. Sepsis remains the primary cause of death from infection despite advances in modern medicine, including vaccines, antibiotics and acute care. In 2011, sepsis represented 5.2% of the national costs for all hospitalizations (nearly 1.1 million hospital discharges) and was also the most expensive condition billed to Medicare, accounting for 6.9% of all Medicare costs. Deaths from sepsis outnumber those from prostate cancer, breast cancer, and AIDS, combined each year. Dissemination of bacteria in the blood results in a cytokine storm, which converts a healthy immune system, normally required to intervene in the case of a blood-borne infection, into a liability for the patient. Sepsis caused by Gram-negative bacteria is, in part, dependent on stimulation of Toll-like receptor 4 (TLR4) by the bacterial membrane component lipopolysaccharide (LPS). The minimal component of LPS necessary for TLR4 stimulation is lipid A, the membrane anchor component of LPS. We have designed preliminary anti-sepsis lipid A (ASLA) based therapeutics using a rudimentary, lipid A:TLR4 structure-activity relationship (SAR) as a guide. Our hypothesis is that refining the SAR for inhibitory lipid A molecules using a rational, evidence-based approach, will lead to effectivel designed ASLA molecules that can protect from Gram-negative sepsis, ultimately improving patient outcomes. To confirm this hypothesis we will: 1) rationally design, characterize, and evaluate lipid-A based therapeutics and 2) employ high resolution mass spectrometry techniques to understand the minimal structural components of lipid A that determine receptor activity and function. Our studies will lead to an advanced understanding of the structural basis for endotoxemia, instructing the design of efficacious ASLA therapeutics for Gram-negative sepsis.